Structural and functional features of the taste system change dramatically during development. While much has been learned by studying normal developmental processes, complementary experiments using experimental manipulations during critical phases of development have been of great value in learning how the taste system is organized. The specific aims of this proposal use genetic knockout mouse models and early dietary manipulations with coordinated techniques of peripheral taste nerve recordings, central nervous system tract tracing, single cell fills of targeted brainstem neurons, in vivo central tast neuron neurophysiology, and in vitro patch-clamp experiments to study the role of activity-independent and activity-dependent factors on gustatory brainstem circuit development. Morphological studies examine 1) the terminal field organization of afferent nerves in the first synaptic relay in the brain, in the nucleus of the solitary tract (NTS), and 2) examine the dendritic characteristics of relay neurons in the NTS that project to the next central relay in mic, and putative inhibitory interneurons. Neurophysiological studies will examine 1) the influences of altered taste-elicited activity during development and early dietary manipulations on taste responses through in vivo single NTS cell recordings, and 2) influences on the intrinsic membrane properties and synaptic properties of NTS cells through in vitro patch- clamp slice recordings. The overall focus of this proposal is on how the central gustatory system is assembled and then refined by experience. Findings from these studies will provide new and important information about the development and plasticity of the peripheral and central gustatory system, and about the development of taste preferences and aversions. They will also be useful in determining the role that the maternal diet and taste-elicited activity have on organizing the developing sense of taste.